Thymic Epithelium Cells Research Articles

Induction of CD40 in promyelocytic HL60 cells cultured with retinoic acid and/or various cytokines.

The antigenic protein CD40 on the surface of B lymphocytes plays an important role in their proliferation, immunoglobulin class switching, and rescue from apoptosis in the germinal center through interaction with T lymphocytes expressing CD40 ligand. The protein is also found on the cell surface of other antigen-presenting cells such as monocytes, dendritic cells, and thymic epithelium cells, but its presence in other myeloid cells has not been reported. We show here that CD40 protein is induced in promyelocytic HL60 cells, when cultured with retinoic acid, a vitamin that converts them to granulocyte-like cells. The cultured cells also expressed CD15, a marker for granulocytes, and cytochrome b(558), an essential component of the superoxide-generating system in phagocytes, on their surface. No detectable amount of mRNA for CD40 was found in naive HL60 cells, whereas a large amount of the message was induced in the cells cultured with the vitamin. Although CD40 expression was enhanced when the cells were further cultured with GM-CSF or IFN-gamma, expression of CD14, a marker for monocytes, was also enhanced. HL60 cells, therefore, express CD40 protein during differentiation not only toward monocytes but also toward granulocytes, at least transiently.

Transplantation tolerance is unrelated to superantigen-dependent deletion and anergy.

C57BL/6 (B6; I-E-, Mls-2b) nude mice, reconstituted at birth with thymic epithelium (TE) from BALB/c (BA; I-E+, Mls-2a) day 10 embryos (E10), permanently accepted BALB/c skin, when grafted as adults. T-cell receptor repertoire analyses in the periphery of these mice revealed no difference in frequencies of I-E/superantigen-reactive T-cell receptor V beta families, as compared to chimeras constructed with syngeneic B6 E10 TE. T lymphocytes bearing V beta 3, V beta 5, and V beta 11 T-cell receptors, from either allogeneic or syngeneic TE chimeras, responded equally well to in vitro receptor-dependent stimulation. Similar results were obtained with nude mice reconstituted at birth with E14 thymuses, already colonized by hemopoietic cells. These observations indicate that neither TE cells nor the progenies of hemopoietic precursors that colonize the thymus up to E14 express or functionally present the superantigens addressed here; it follows that tolerance to skin grafts and superantigen-related T-cell deletions are unrelated phenomena.

Culture and characterization of thymic epithelium from autoimmune NZB and NZB/W mice

Autoimmune NZB and NZB/W mice display early abnormalities in thymus histology, T cell development, and mature T cell function. Abnormalities in the subcapsular/medullary thymic epithelium (TE) can also be inferred from the early disappearance of thymulin from NZB. It has also been reported that NZB thymic epithelial cells do not grow in culture conditions that support the growth of these cells from other strains of mice. In order to study the contribution of TE to the abnormal T cell development and function in NZB and NZB/W mice, we have devised a culture system which supports the growth of TE cells from these mice. The method involves the use of culture vessels coated with extracellular matrix produced by a rat thymic epithelial cell line, TEA3A1, and selective low-calcium, low-serum medium. In addition TEA3A1 cells have been used as an antigen to generate monoclonal antibodies specific for subcapsular/medullary TE. These antibodies, as well as others already available, have been used to show that the culture conditions described here select for cells displaying subcapsular/medullary TE markers, whereas markers for cortical TE and macrophages are absent.

Lack of transformation of murine thymocytes by thymic epithelium

THE normal thymus consists of two basic components: a reticular–epithelial component derived from the third and fourth bronchial pouches1 and a lymphoid component from stem cells which migrate into the embryonal thymus from fetal liver2 and later from bone marrow3. Two types of thymic reticular cells have been observed by electron microscopy: epithelial reticular cells and mesenchymal reticular cells or macrophages. The villous epithelial cells of the cortex and the cystic epithelial cells of the medulla were shown to be important for T cell differentiation4. Cultures of thymus epithelial cells were shown to induce the differentiation of precursor cells into certain mature T lymphocytes5,6. Recent studies have suggested that thymic epithelium cells (derived from leukaemic thymus) were capable of providing the leukaemogenic signal and thereby inducing in vitro leukaemia transformation of normal thymocytes. Thus, it was claimed that young AKR thymocytes cultured on thymus epithelium monolayers from aged AKR mice could induce leukaemia when injected into normal young recipients7. Similarly, monolayers of thymus epithelium cells, derived from radiation leukaemia virus-induced thymomas in C57BL/6 mice could bring about transformation of normal C57BL/6 thymocytes, thereby demonstrating in vitro leukaemogenesis8. Our aim here was to study further the possible role of the thymic epithelial reticulum (TER) in leukaemogenesis and we present evidence that the leukaemic cells are not derived from the thymus lymphocytes, nor from a ‘transformation capacity’ of the epithelial cells themselves, but that they are already present within phagocytic TER cells. We used the thymic epithelium monolayer–thymocyte co-cultivation method7,8 and the transplantation bioassay genotype analysis method9 (used to demonstrate the origin of the developing leukaemias following injection of thymocytes or thymic epithelium cells into appropriate recipients).